Biology subjects

Rehorova, M.

Publications and source records attributed to Rehorova, M..

4 recordsLinked to original sources

bioRxiv2026

Longitudinal Imaging in a Mouse Model of Focal Cortical Dysplasia Reveals Lesion Expansion and Loss of Pre-Discharge Neuronal Recruitment

ABSTRACT Objective: Focal cortical dysplasia type II (FCD II) is a leading cause of drug-resistant focal epilepsy, yet how its lesional circuits behave and change over time in vivo has not been directly observed. Methods: We used a mouse model of FCD II carrying the patient-derived gain-of-function mTORp.L2427P variant introduced by in utero electroporation. Through a chronic cranial window over the lesion, we performed repeated in vivo two-photon calcium imaging of identified dysmorphic neurons, pyramidal cells, and VIP interneurons at defined time points, combined with video-EEG monitoring, to determine seizure status and relate cellular activity to interictal discharges. Results: The lesion was not static in adulthood. Dysplastic cortex expanded progressively. This expansion occurred without the tenascin R/C accumulation reported in human FCD II, and was partly explained by continued somatic growth of dysmorphic neurons. Dysmorphic neurons were generally hypoactive; in seizing mice, both dysmorphic and pyramidal cell activity progressively declined, whereas VIP interneuron activity increased slightly in non-seizing animals. In non-seizing lesional cortex, neurons were reliably recruited immediately before interictal discharges. By late disease stages, pre-discharge recruitment had weakened to the point that lesional layer 2/3 neurons were no more active before discharges than expected by chance. Significance: These findings recast FCD II as a lesion that continues to remodel structurally and functionally throughout adulthood, and does so most markedly in animals with seizures. Growth, a cell-type-specific shift in spontaneous activity, and a progressive loss of the lesion's temporal lead over interictal discharges together suggest that FCD II is a dynamically evolving lesion whose relationship to epileptiform activity changes over time. If the lesion progressively loses its generative role, the window in which removing it can arrest the disease is finite, consistent with clinical evidence favoring earlier surgery.

neuroscience↗

bioRxiv2026

Dasatinib-Quercetin May Reduce Senescence Markers, Without Senolysis or Seizure Modification, in a Mouse Model of Focal Cortical Dysplasia

Mounting evidence from surgical type II focal cortical dysplasia (FCD) tissues and mouse models have recently shown that dysmorphic neurons carrying MTOR mutations (DNs) in FCD exhibit hallmarks of cellular senescence. Building on pioneering work from the Baulac group identifying cellular senescence as a feature of mTOR-pathway FCD, a recent study by Ribierre et al. (2024) [1] proposed oral dasatinib and quercetin (DQ) as a therapy that partially decreases the load of mutant, senescent neurons and thus reduces seizure occurrence in FCD mice. Using a different mouse strain and a different gain-of-function mutation in MTOR, our data confirm the presence of senescence hallmarks in FCD mice, but do not support one of the conclusions of Ribierre et al.--that DQ acts as a senolytic in an FCD mouse model--and we propose an alternative interpretation. We longitudinally tracked individual cell fate using two-photon microscopy and complemented these data with EEG monitoring and immunohistochemistry. Immunohistochemical analyses were performed within the same sections using multiple markers, allowing direct identification of mutant neurons and assessment of senescence-associated labeling. While we observed a detectable reduction in a senescence-associated marker, consistent with a senomorphic effect, it did not translate into a change in seizure phenotype, despite treatment timing and dosing matching those in the original study. For detailed materials and methods, see Extended Methods.

neuroscience↗

bioRxiv2025

SEIZURE OCCURRENCE IN FCD TYPE II IS PREDICTED BY LESION POSITION AND LINKED TO CYTOARCHITECTURAL ALTERATIONS

Focal cortical dysplasia (FCD) is a common malformation of cortical development and a major cause of early-onset, drug-resistant epilepsy. FCD type II is defined by abnormal lamination, altered cellular composition, and pathological cells, notably dysmorphic neurons (DNs) and balloon cells. DNs are thought to drive epileptogenicity through both cell-autonomous and non-cell-autonomous mechanisms, the latter including not only aberrant connectivity but also indirect modulation of excitability in local cell populations. We performed a multiscale structural and morphological analysis to elucidate the basis of FCD epileptogenicity and the impact of somatic mTOR mutations during brain development. Using a mouse model of FCD type II, we show that lesions in frontal and motor cortical regions are the strongest predictors of spontaneous seizure occurrence. This localization-dependent epileptogenicity offers an experimental explanation for the higher clinical epileptogenicity of frontal FCDs and suggests that posterior lesions may remain silent--an open question in human pathology. In our model, FCD tissue displayed considerable expansion, with cortical thickness up to [~]20% in seizure-bearing animals. This expansion coincided with an overall [~]40% reduction in neuronal density, consistent with tissue hypertrophy. DN density did not differ between seizure and non-seizure animals, challenging the notion that higher DN load directly predicts epileptogenesis. At the microscopic level, we describe DN axonal pathologies, including giant varicosities. In the cortex, these appeared as vesicle-filled boutons, whereas along callosal axons they were frequent but largely empty. Bouton density was markedly reduced in FCD cortex. Together, these findings leave the net synaptic effect of dysmorphic neurons unresolved, challenging the assumption that axonal hypertrophy translates into increased excitatory drive. While morphological abnormalities in FCD type II are well documented, their functional consequences remain incompletely understood. Here, we used macro- and microscopic structural features of FCDII to assess seizure susceptibility, providing new insights into epileptogenesis.

neuroscience↗

bioRxiv2021

Sensitivity optimization of a rhodopsin-based fluorescent voltage indicator

The ability to optically image cellular transmembrane voltage at millisecond-timescale resolution can offer unprecedented insight into the function of living brains in behaving animals. The chemigenetic voltage indicator Voltron is bright and photostable, making it a favorable choice for long in vivo imaging of neuronal populations at cellular resolution. Improving the voltage sensitivity of Voltron would allow better detection of spiking and subthreshold voltage signals. We performed site saturation mutagenesis at 40 positions in Voltron and screened for increased {Delta}F/F0 in response to action potentials (APs) in neurons. Using a fully automated patch-clamp system, we discovered a Voltron variant (Voltron.A122D) that increased the sensitivity to a single AP by 65% compared to Voltron. This variant (named Voltron2) also exhibited approximately 3-fold higher sensitivity in response to sub-threshold membrane potential changes. Voltron2 retained the sub-millisecond kinetics and photostability of its predecessor, with lower baseline fluorescence. Introducing the same A122D substitution to other Ace2 opsin-based voltage sensors similarly increased their sensitivity. We show that Voltron2 enables improved sensitivity voltage imaging in mice, zebrafish and fruit flies. Overall, we have discovered a generalizable mutation that significantly increases the sensitivity of Ace2 rhodopsin-based sensors, improving their voltage reporting capability.

neuroscience↗